Many types of cartons formed from folded paperboard or the like have been developed over the years. These cartons fall into two major groups, namely those which use interlocking corners and tabs to secure cartons in their erected position, and those which have an adhesive coating applied to selected portions of the paperboard blank which, erected, are secured in their erected position by the adhesive bond which forms therebetween.
Machinery for folding and erecting both types of paperboard blanks is highly developed. Specially designed machines handle a number of complex operations which must be performed to erect and secure the cartons. Carton blanks which are to be adhesively bonded generally include at least a base panel, wall panels attached to the base panel, and gussets or glue panels formed at the corners of the wall panels. Adhesive is coated on the glue panels or, alternatively, on portions of the wall panels adjacent the glue panels, and the carton walls and glue panels erected and folded into contact with one another and secured together for a time sufficient to allow the adhesive to set.
Prior art machines for performing such carton-forming and gluing operations are exemplified by the patent to Hoyrup, U.S. Pat. No. 3,626,819, issued on Dec. 14, 1971, and assigned to the assignee of the present invention. This patent shows a vertically reciprocating plunger disposed above a carton-forming die. A movable frame or carrier having suction cup means transfers the carton blank from a stack into contacting registration with the upper surface of the carton-forming die. The die includes a number of vertical posts and walls for controllably erecting and folding wall panels of a carton blank disposed over the die when the carton blank is forced therein by the motion of the plunger. Spots or stripes of adhesive are applied to the undersurface of the blank at the die mouth by daubing applicators which rise from pots of liquid adhesive disposed next to the die. One disadvantage of this prior art type of apparatus is that it cannot accommodate the complex and high speed folding and gluing operations which must be performed to form a hinged, clam-shell type carton.
Clam-shell type cartons have two sections, each section including a base panel, wall panels attached to the base panel, and corner panels formed at the corners of the wall panels, with the two sections separated by an articulated hinge, and tab or glue panels formed adjacent the hinges. Such cartons are useful, for example, as containers for fast food items such as hamburgers and the like. The paperboard from which the carton is formed is normally printed with attractive graphics and coated (with a polyethylene coating or the like) to protect the product and prevent absorption of liquid or food juices by the paperboard.
Cartons of the clam-shell type present one particularly difficult forming problem not present when simple trays are being formed. That is, some means must be provided to fold and gather the articulated hinge of the carton blank in the same harmonic motion that is used for the remainder of the folding and gluing steps. Furthermore, the glue panels and tabs adjacent the hinge must be prebroken and carefully controlled so as to lie within the interior of the carton against the preglued areas of the carton walls when the carton is folded and erected by the reciprocating plunger.
Thus, it would be desirable and most efficient to provide apparatus for forming a clam-shell style carton with some means for rapidly and controllably folding and gathering the articulated hinge without adversely affecting the accurate positioning and retention in registration of the blank carton-forming die. The carton-forming apparatus must include means for controllably prebreaking and retaining selected areas of the carton blank prior to full erection of the carton walls. The hinge folding and carton blank prebreaking means should be constructed so as to not interfere in any way with the operation and high speed, harmonic motion of the carton-forming plunger.